Thread tensioning control for sewing machines



May 31, 1960 G. s. ARMSTEAD, JR 2,933,479

THREAD TENSIONING CONTROL FOR sswmc MACHINES Filed Dec. 11. 1956 m t m nm M e H United States Patent THREAD TENSIONING CONTROL FOR SEWING MACHINES George B. Armstead, Jr., Glastonbury, Conn., assignor to The Merrow Machine Company, Hartford, Conn., a corporation of Connecticut Filed Dec. 11, 1956, Ser. No. 627,707

9 Claims. (Cl. 112-254) This invention relates to sewing machine thread tensioning devices and more particularly to means whereby the tension on one or more threads of a sewing machine may be automatically applied or released.

In the application of stitching to a piece of work introduced into a sewing machine (that is between the presserfoot on one side and the work support and feed dog or dogs on the other side) a length of threads extends between the last formed stitch and the stitch forming implements and as the work piece passes from beneath the presserfoot a length of threads, enchained or otherwise, extends from the end of the work piece to the stitching implements. It may be desirable that an operator draw the stitched piece of work a certain distance beyond the rear of the presserfoot before severing the threads extending therefrom to the stitching implements.

For example, in a two-needle sewing machine, one of the needle threads may not be included in a chain of other thread, thus when an operator draws a work piece away from the rear of the presserfoot, that thread that is not enchained is subjected to considerable strain and may be broken, thereby causing vexatious delay in resuming the stitching ofone piece of work after another.

A primary object of the invention is to provide a thread tension device which is automatically controlled by the work material.

More specifically, an object of the invention is to provide a thread tensioning device which is effective only when work is engaged between the presserfoot and the support.

A feature of the invention resides in an arrangement wherein an element of an electro-magnet is suitably located adjacent to a tension disk that is one of a pair of disks comprising a form of tension device commonly employed for sewing machine thread control. This magnet is energized, when there is no work material between the presserfoot and the work support, to move the near tenison disk away from its companion stationary disk against the urge of the usual spring by which suitable tension is normally imposed upon a thread trained between the disks.

As the tension disk adjacent the magnet moves away from the stationary disk, tension on thread therebetween is released.

Other objects and advantages of my invention will become apparent by reference to the following specification taken in conjunction with the accompanying drawings.

In the drawings:

Fig. 1 is a fragmentary front end view, partly in section, of a sewing machine including mechanism comprising my invention;

Fig. 2 is a view of the structure shown in Fig. l as viewed from the left;

Fig. 3 is an enlarged detail view with parts shown in section substantially on line 3-3 of Fig. 1; and

Fig. 4 is a detail view similar to Fig. 3 but showing a further enlargement of certain parts shown in Fig. 3.

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Referring to the drawings, my invention is shown incorporated in a sewing machine of the Merrow type. Certain parts of the machine illustrated may be described briefly as follows: 1 designates the machine frame, 2 the work support and 3 the head which is suitably secured to frame 1. Stitch forming implements include curved needles 5 and 6 arranged to cooperate with loopers (not shown) to form overedge stitching. For certain types of work, needles 5 and 6 are substituted for a single needle. In an arrangement employing two needles the thread of one of the needles is not included with thread enchained by the other needle and loopers as when the sewing machine is running but with no work in position for re ceiving stitching.

Feeding mechanism as shown includes feed dogs 7 and 8. These cooperate with presserfoot '9 carried by a presser arm 10. To permit such movement of the presserfoot as that imparted thereto by feed dogs 7 and 8 as they are projected above the work support 2, the presser arm 16 is mounted on a rocker 11 journaled on a shaft 12. A pivotal connection is formed between rocker 11 and presser arm 10 by a stud 13. For moving presser arm 10 and thereby yieldingly urging the presserfoot toward the work support 2, a presser bar 14 and spring 15 are provided and may be partly enclosed in support 16 which forms a part of head 3. Latch actuating means are indicated in a general way by 20 and provide for releasing presser bar 14 from presser arm 10 so that the arm may be swung about its pivotal support 13 to carry presserfoot 9 away from its normal position above the work support to afford convenient access to stitch forming implements.

A needle thread tension device 21 includes a rod 22 extended from head 3 and terminating in a threaded stem 23. Tension disks 24 and 25 are mounted on rod 22 with disk 25 fastened rigidly to the rod while disk 24 is axially movable along the rod to and from disk 25. Tension spring 26 surrounds rod 22 between movable disk 24 and an adjusting nut 27 threaded on stem 23. Adjustment of nut 27 serves to impose suitable normal tension on a thread T passing between disks 24 and I 25, such for example, as may be required while stitching is being applied to work material passing between the presserfoot on one side and the feed dogs and work support on the other side. Jamb nut 28 serves to secure a suitable adjustment of nut 27.

To release tension on thread trained between disks 24 and 25, as may be required when work material has passed from beneath the presserfoot, an electro-magnet 29 is placed with its pole pieces 30 and 31 in suitable position relative to movable tension disk 24, which is constructed from a magnetically soft material, so that when the magnet is energized, disk 24 is moved away from stationary disk 25. In effect, disk 24 may be said to be the armature of electromagnet 29.

An electric circuit 32 includes a suitable power source such as battery 32a from which magnet 29 may be energized. Circuit 32 is grounded to the machine frame 1 as at 33 and includes a contact 34 carried by presserfoot 9. Contact 34 comprises a bolt having a slightly tapered head 35 and a threaded stem 36 to receive nut 37. A bushing 38 of insulating material separates contact 34 from presserfoot 9 but leaves the head end of the contact exposed and opposite work engageable surface of work support 2.

Thus when work material is between the presserfoot and work support 2 -it serves to open circuit 32 and deenergize magnet 29 thereby leaving disk 24 free. to be moved toward disk 25 by spring 26, thus placing tension -on thread passing between disks 24 and 25. On the other hand when work material passes or is removed from between presserfoot 9 and work support 2, contact 34 is grounded upon work support 2 thereby closing circuit 32 to energize magnet 29 thus causing tension disk .24 to move away. from tension disk 25 so that thread tension is released.

Electro-magnet 29 may be supported in any suitable manner, as shown it is mounted on a bracket 39 which is secured to machine frame 1 as by screws 40.

While I have shown a specific embodiment of my invention, it will be apparent to those skilled in the art that the disclosed embodiment is capable of modification. Therefore, the foregoing description is to be considered exemplary rather than limiting and the true scope of my invention is that defined in the following claims.

What I claim is:

1. In a sewing machine having a frame including a work support, a presserfoot movably mounted on said frame, and means for yieldably urging said presserfoot toward said work support to clamp work material upon the work support; a thread tension device mounted on said frame and comprising a pair of thread engaging disks, spring means for urging one of said disks toward the other disk to impose tension upon a thread trained between said disks, an electro-magnet supported from said frame adjacent one of said disks and operable when en ergized to move said one of said disks away from the other disk, a contact carried by the presserfoot engageable with said work support in the absence of work material between said presserfoot and said work support, and an electric circuit including said contact, work support and electro-magnet, said circuit being connected to energize said electromagnet when said contact engages said work support.

2. In a sewing machine having a frame including a work support, clamping means movable toward and away from said work support for clamping work material upon said work support, and stitch forming means including means for supplying thread thereto; thread tensioning means comprising a pair of relatively movable members mounted upon said frame for frictional gripping engagement with thread passing to said stitch forming means, means biasing said movable members toward each other to grip thread therebetween and thereby apply tension to thread passing to said stitch forming means, tension release means actuable to move said members away from each other to thereby release tension upon said thread, and control means mounted upon said clamping means for actuating said tension release means in response to removal of work material from between said clamping means and said work support.

3. In a sewing machine as recited in claim 2, wherein said tension release means comprises an electro-magnet operable when energized to move said movable members away from each other, and said control means comprises an electric contact engageable with said work support in the absence of work material between said clamping means and said support, and means responsive to the engagement of said contact with said work support for energizing said electro-magnet.

4. In a sewing machine having a frame, a work support mounted upon said frame, a presserfoot mounted upon said frame for movement toward and away from said work support to clamp work material upon said work support, and stitch forming mechanism including -,thr.ead, normally inactive tension release means mounted upon said frame adjacent one of said members and aetuable to move said one of said members away from the other of said members to thereby release tension on said thread, and control means mounted upon said presserfoot for actuating said tension release means, said control means being connected to said tension release to maintain said tension release means in its normally inactive condition while work material is located between said presserfoot and said work support and to actuate said tension release means in response to removal of work material from between said presserfoot and said work support. p

5. -In a sewing machineasrecited in claim 4 wherein said tension release means comprises an electromagnet operable when energized to move said one of said members away from the other of said members, and said control means comprises an electric circuit connected to energize said electromagnet upon contact between said presserfoot and said work support.

6. In a sewing machine having a metal frame including a work support, a presserfoot movable toward and away from said work support forclamping work material upon said support, and stitch forming means including means for supplying thread thereto; thread tensioning means comprising a pair of relatively movable members mounted upon said frame for frictional gripping engagement with thread passing to said stitch forming means, means biasing said members toward each other to grip said thread therebetween and thereby apply tension to said thread, an electro-magnet operable when energized to separate said members to thereby release tension upon said thread, and means for energizing said electro-magnet comprising a contact mounted upon said presserfoot for engagement with said work support in the absence of work material between said presserfoot and said work support, an electrical power source and a series circuit connecting said contact to said frame through said source and said electro-magnet.

7. A thread tensioning control for thread passing to the stitch forming mechanism of a sewing machine comprising a pair of opposed relatively movable thread ongaging members adapted to frictionally grip thread passing to said stitch forming mechanism, spring means biasing said members toward each other, eelctro-magnetic means operable when energized to separate said members to thereby release tension on thread passing between said members to said stitch forming mechanism, and means controlled by the relationship of work material to said stitch forming mechanism for maintaining 50 said" electro-magnetic means de-energized when work material is located in operative relationship to said stitch forming mechanism and to energize said electro-magnetic means in the absence of work in operative relationship to said stitch forming mechanism.

8. A thread tensioning control for thread passing to the stitch forming means of a sewing machine comprising a fixed first thread engaging member, a second thread engaging member of magnetically soft material mounted for movement toward and away from said first thread engaging member, said thread engaging members being located in a position to frictionally grip thread passing between said members toward said stitch forming mechanism, spring means biasing said second thread engaging member toward said first thread engaging member, electro-magnetic means operable when energized to move said second thread engaging member away from said firstthread engaging members to thereby release tension on thread passing through said members, means for detecting the presence of work material in operative relationship to said stitch forming mechanism, and means operable by said detecting means for maintaining said electro-magnetic means de-energized when work material is located in operative relationship to stitch forming mechanism and for energizing said electromagnetic means in the absence of work material in operative relationship to said forming mechanism.

9. In a sewing machine having a frame, work fabric supporting means mounted upon said frame, means for forming a stitch in work fabric on said supporting means, and means for supplying thread to said stitch forming means; a thread tensioning device comprising a pair of relatively movable members mounted upon said frame for movement toward and away from each other, said members being located to frictionally grip therebetween thread passing to said stitch forming means, tension release means mounted upon said frame for moving one of said thread gripping members away from the other thread gripping member to thereby release tension on said thread, and work fabric controlled means mounted upon the frame for actuating said tension release means in response to the absence of fabric at said stitch forming means.

References Cited in the file of this patent UNITED STATES PATENTS 1,518,494 Elcock Dec. 9, 1924 1,592,116 Lindgren July 13, 1926 2,582,211 Turner Jan. 8, 1952 2,698,590 Garbe Jan. 4, 1955 FOREIGN PATENTS Austria Oct. 25, 1910 

